Low-temperature synthesis of homogeneous solid solutions of scheelite-structured Ca_1−xSr_xWO₄ and Sr_1−xBa_xWO₄ nanocrystals

Abstract

A series of compositionally complex scheelite-structured nanocrystals of the formula A1-xAWO4 (A = Ca, Sr, Ba) have been prepared under benign synthesis conditions using the vapor diffusion sol-gel method. Discrete nanocrystals with sub-20 nm mean diameters were obtained after kinetically controlled hydrolysis and polycondensation at room temperature, followed by composition-dependent thermal aging at or below 60 °C. Rietveld analysis of X-ray diffraction data and Raman spectroscopy verified the synthesis of continuous and phase-pure nanocrystal solid solutions across the entire composition space for A1-xAWO4, where 0 ≤ x ≤ 1. Elemental analysis by X-ray photoelectron and inductively coupled plasma-atomic emission spectroscopies demonstrated excellent agreement between the nominal and experimentally determined elemental stoichiometries, while energy dispersive X-ray spectroscopy illustrated good spatial elemental homogeneity within these nanocrystals synthesized under benign conditions.

Studying Catalytically Viable Single-Crystalline Metal Oxide Nanorods Using Synchrotron-Based Scanning Hard X-ray Microscopy

“…To summarize, with respect to peak positions, binding energy values for Ba 3d and W 4f remained essentially unchanged within all of our as-synthesized tungstates, suggesting that the nominal oxidation states of not only the tungstate cation (i.e., +6) but also the alkaline earth metal cations (i.e., +2) did not dramatically alter across the different sample series. Indeed, our data support the assumption that Ba ions can be readily substituted by Sr ions within stable configurations . Overall, these data are consistent with conservation of the electronic integrity of the underlying tungstate lattice, which was maintained even after Sr substitution of Ba.…”

“…Indeed, our data support the assumption that Ba ions can be readily substituted by Sr ions within stable configurations. 33 Overall, these data are consistent with conservation of the electronic integrity of the underlying tungstate lattice, which was maintained even after Sr substitution of Ba.…”

Sr1/2Ce5/14□1/7WO4: a new modulated ternary scheelite compound

“…Most of them are built with a charge difference of 2 between A and A 0 cations such as (Ag,RE)(MoO 4 ) 2 and (Li, RE)(MoO 4 ) 2 , where RE is a rare earth element (Abakumov et al, 2014). The charge difference is usually accommodated by cation vacancies on A sites, with or without cation ordering or incommensurate modulations (Abakumov et al, 2014;Albino et al, 2012;Culver et al, 2015). Ternary scheelites with a charge difference of 1 are uncommon, and apart from a lead-lanthanide-based compound (Takai et al, 2004), only (Ca, Eu)(BO 4 ) 2 and (Sr,Eu)(BO 4 ) 2 have been extensively studied (Abakumov et al, 2014;Jiang et al, 2015).…”

Cation-Induced Variation of Micromorphology and Luminescence Properties of Tungstate Phosphors by a Hydrothermal Method

“…Among inorganic phosphors, divalent tungstates have attracted more attention in recent years because of their excellent spectra, stable chemical properties, wide intrinsic spectra, and high average refractive indices . Meanwhile, as a kind of typical self-activating material, tungstates exhibit high-efficiency blue emission under ultraviolet light excitation due to the charge transfer between activated 2p orbitals of O 2– and the empty orbitals of the central W 6+ ions in the host materials .…”

“…Among inorganic phosphors, divalent tungstates have attracted more attention in recent years because of their excellent spectra, stable chemical properties, wide intrinsic spectra, and high average refractive indices. 1 Meanwhile, as a kind of typical self-activating material, tungstates exhibit high-efficiency blue emission under ultraviolet light excitation due to the charge transfer between activated 2p orbitals of O 2− and the empty orbitals of the central W 6+ ions in the host materials. 2 As a result, tungstates with excellent physicochemical character have been extensively investigated and show potential applications in medical devices, 3 microwaves, 4 humidity sensors, 5 catalysts, 6−9 scintillates, 10 phototropism, 11 and white light-emitting diodes (wLEDs).…”